<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<script type="text/javascript">
			
			// var myName = '刘德华';
			// console.log("myName: "+myName)
			
			var myName  ;  //name 没有赋值，没有初始化
			console.log(myName) ; // undefined  变量声明，未初始化 

			console.log( "typeof(myName) : "+typeof(myName))
			
			var myAge = 18;
			console.log( "myAge: "+myAge)
			myAge = null;
			console.log( "myAge: "+myAge)
			console.log( "typeof(myAge) : "+typeof(myAge)) ; // null值的typeof类型为 object
			
			
			
		</script>
	</head>
	<body>
	</body>
</html>
